The lower respiratory tract is protected from infectious agents by the mucociliary apparatus, by pulmonary macrophages, and by soluble factors in pulmonary secretions. Considering the large surface area in the lung, antimicrobial factors in tracheobronchial secretions and alveolar lining material would provide an efficient mechanism to eliminate microbial challenges which occur during minor aspirations. Alterations in these antimicrobial factors may have a role in the pathogenesis of infection during certain disease states but this possibility has not been studied. The experiments described in this proposal will characterize a candidacidal factor recently identified in murine bronchoalveolar lavage fluid. These studies will involve partial purification of this factor(s), determination of its molecular weight, testing it against a panel of Candida spp, and evaluation of other possible functional activities (including opsonic and procidal). Other experiments will investigate its mechanism of action, its cellular origin in the lung, and the effect of various chemotherapeutic and immunosuppressive agents on its presence and concentration. These experiments will involve animal studies and biochemical/tissue culture studies. In addition, human bronchoalveolar lavage fluid will be tested for this activity. These experiments should expand a developing area of research in pulmonary host defense processes and should help clarify the importance of soluble antimicrobial factors in the lung.